1. Field of the Invention
The present invention relates to multilayered LC filters, and more specifically, to a multilayered LC filter for use in a mobile communication devices such as a cellular phone.
2. Description of the Related Art
As an example of such a multilayered LC filter, FIG. 8 shows the construction of a conventional multilayered LC filter 1. The multilayered LC filter 1 includes a laminated body 2 composed of laminated insulating sheets, and within the laminated body 2, inductors L1 and L2 defined by inductor via holes provided in ceramic sheets and connected to each other, and capacitors C1 and C2 that are defined by hot-side capacitor patterns 3 and 4 and a ground-side capacitor pattern 7.
One end of the inductor L1 is electrically connected to an external ground electrode G1 via an internal ground pattern 5, and the other end thereof is electrically connected to the hot-side capacitor pattern 3. Similarly, one end of the inductor L2 is electrically connected to an external ground electrode G2, provided on the surface of the laminated body 2, via an internal ground pattern 6, and the other end thereof is electrically connected to the hot-side capacitor pattern 4. The hot-side capacitor patterns 3 and 4 are electrically connected respectively to an external input electrode and an external output electrode (not shown) provided on the surface of the laminated body 2.
In the multilayered LC filter 1, the inductor L1 and the capacitor C1 define an LC resonator Q1. Similarly, the inductor L2 and the capacitor C2 define an LC resonator Q2. Because the internal ground patterns 5 and 6 are electrically separated, the ground sides of the two LC resonators Q1 and Q2 are not combine-coupled, but instead are electrically independent of each other. Thus, the coupling between the resonators Q1 and Q2 is capacitive and weak, with the value of the equivalent magnetic coupling being 0.1 or smaller.
As another example, FIG. 9 shows the construction of another conventional multilayered LC filter 11. The multilayered LC filter 11 includes a laminated body 12 including laminated ceramic sheets, and within the laminated body 12, inductors L1 and L2 are defined by inductor via holes provided on insulating sheets and connected to each other, and capacitors C1 and C2 are defined by hot-side capacitor patterns 13 and 14 and a ground-side capacitor pattern 16.
First ends of the inductor L1 and the inductor L2 are electrically connected respectively to external ground electrodes G1 and G2 via an internal ground pattern 15, and second ends thereof are electrically connected respectively to the hot-side capacitor patterns 13 and 14. The hot-side capacitor patterns 13 and 14 are electrically connected respectively to an external input electrode and an external output electrode (not shown) provided on the surface of the laminated body 12.
In the multilayered LC filter 11, the inductor L1 and the capacitor C1 define an LC resonator Q1. Similarly, the inductor L2 and the capacitor C2 define an LC resonator Q2. The ground sides of the two resonators Q1 and Q2 are combine-coupled via an internal ground pattern 15, thus being electrically short-circuited. Thus, the coupling between the LC resonators Q1 and Q2 is inductive and strong, with the value of the equivalent magnetic coupling being 0.2 or larger.
However, although the conventional multilayered LC filters 1 and 11 can provide a value of the magnetic coupling between the LC resonators Q1 and Q2 of 0.1 or smaller, or 0.2 or larger, they fail to provide a value of the magnetic coupling between 0.1 and 0.2. It is known that, for example, in the multilayered LC filter 1 shown in FIG. 8, the value of the magnetic coupling between the LC resonators Q1 and Q2 can be adjusted by changing the distance between the inductors L1 and L2. However, this method of adjusting the value of the magnetic coupling by changing the distance between the inductors L1 and L2 does not allow for selecting an arbitrary value of the magnetic coupling due to restrictions of the product size, and other limitations. For example, the distance between the inductors L1 and L2 may be shortened to a certain extent to adjust the value of the magnetic coupling between the LC resonators Q1 and Q2. However, when the inductors L1 and L2 come too close to each other, problems may occur in the manufacturing process. For example, the ceramic material between the inductors L1 and L2 may crack at the time of firing.
In order to overcome the problems described above, preferred embodiments of the present invention provide a multi-layered LC filter which allows adjustment of the value of the magnetic coupling between LC resonators without changing the size of the filter.
According to a preferred embodiment of the present invention, a multi-layered LC filter includes a laminated body having a plurality of insulating layers that are stacked on each other. In the laminated body, a plurality of LC resonators including a plurality of inductors and a plurality of capacitors is provided. The multi-layered LC filter includes a plurality of via holes connected to each other in the lamination or stacking direction of the plurality of insulating layers, and a plurality of external ground electrodes provided on a surface of the laminated body, to which first ends of the plurality of inductors are electrically connected individually, and a bridge pattern disposed on a surface of one of the plurality of insulating layers and in proximity to the plurality of inductors, electrically connecting the plurality of external ground electrodes.
In accordance with another preferred embodiment of the present invention, a multi-layered LC filter includes a laminated body having a plurality of insulating layers stacked on each other. In the laminated body, a plurality of LC resonators having a plurality of inductors and a plurality of capacitors is provided. The multi-layered LC filter includes a first insulating layer on which segmented internal ground patterns are provided, a second insulating layer on which a plurality of inductor via holes and a bridge pattern in proximity to the plurality of inductor via holes are provided, a third insulating layer on which a plurality of inductor via holes is provided, a fourth insulating layer on which a plurality of hot-side capacitor patterns is provided, a fifth insulating layer on which a ground-side capacitor pattern is provided opposing the plurality of hot-side capacitor patterns, so as to form the plurality of capacitors of the plurality of LC resonators, and an external input electrode, an external output electrode, and a plurality of external ground electrodes provided on a surface of the laminated body which includes first to fifth insulating layers laminated. In the multilayered LC filter, the plurality of inductor via holes provided in the second insulating layer and the plurality of inductor via holes provided in the third insulating layer are connected to each other in the lamination direction of the plurality of insulating layers. First ends of the plurality of inductors are electrically connected to the plurality of hot-side capacitor patterns of the plurality of capacitors, and second ends thereof are electrically connected to the plurality of external ground electrodes via the internal ground patterns provided on the first insulating layer. The ends of the bridge pattern provided on the second insulating layer are electrically connected respectively to the plurality of external ground electrodes, and the bridge pattern is disposed in proximity to the plurality of inductors including the plurality of via holes.
The plurality of inductors primarily includes the plurality of via holes connected with each other. Although, for example, the internal ground patterns have respective inductive elements, the primary inductive elements of the inductors are associated with the plurality of via holes. The via holes are arranged to function as inductors when represented in terms of an equivalent circuit.
The bridge pattern electrically connecting the plurality of external ground electrodes is disposed in proximity to the plurality of inductors including the plurality of via holes, so that the value of the equivalent magnetic coupling between the plurality of LC resonators can be adjusted by changing the position of the bridge pattern. If the bridge pattern is disposed between the ends of each of the plurality of inductors in the lamination or stacking direction of the plurality of insulating layers, the value of the magnetic coupling between the plurality of LC resonators becomes larger than about 0.1 and smaller than about 0.2. That is, the value of the magnetic coupling between the plurality of LC resonators is larger than that in the case where the LC resonators are inductively coupled, and larger than that in the case where the LC resonators are capacitively coupled.
According to preferred embodiments of the present invention, the bridge pattern electrically connecting the plurality of external electrodes is preferably disposed in proximity to the plurality of inductors, so that the value of the equivalent magnetic coupling between the plurality of LC resonators can be adjusted by changing the position of the bridge pattern without changing the size of the filter.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the detailed description of preferred embodiments with reference to the attached drawings.